PASADENA, Calif. — The incidence of chorioamnionitis — an infection of the amniotic fluid, fetal membranes and placental tissues, and one of the most frequent causes of preterm birth and infant illness — more than doubled between 1995 and 2010, according to a Kaiser Permanente Southern California study published today in the International Journal of Reproductive Medicine.

The study examined 471,821 single-child births at Kaiser Permanente hospitals in Southern California over a 15-year period. Researchers examined electronic health records and information from infant birth certificates, including maternal demographics, behavioral characteristics, labor and delivery complications, and additional clinical data. Researchers found that the incidence of chorioamnionitis rose from 2.7 percent of births in 1995-96 to 6.0 percent of births in 2009-10, a relative increase of 126 percent.

While fetal membrane infection rates rose for women of all races and ethnicities, Hispanic and Asian women had the most dramatic increases. Infection rates for Asian women increased by 151 percent, and rates for Hispanic women rose by 145 percent. White women also experienced a marked increase of 141 percent. The increase in this infection was lowest among African-American women at 66 percent.

“This study provides new insight into the occurrence of chorioamnionitis that can help physicians understand how diagnosis rates differ by race, ethnicity, and gestational age at delivery,” said study lead author, Michael Fassett, MD, a maternal fetal specialist at Kaiser Permanente West Los Angeles Medical Center. “We studied a very large, diverse, and representative population of women giving birth so we now know that there has been a significant increase in chorioamnionitis that has affected women from all race and ethnic groups.”

Researchers also found women who had labor induced for medical reasons had the highest rates of fetal membrane infections, followed by women who were induced without an obvious medical reason. During the study period, the rate of labor induction increased by 46 percent.

“Generally, when women undergo labor induction, they experience longer labor and more cervical examinations, which increases their risk for infection,” said Dr. Fassett. “It is important to remember that there are medical conditions for which the benefits of medically-induced labor far outweigh the potential risks. Patients should work with their doctors to make the best choice about labor induction for the mother and the baby.”

Chorioamnionitis is caused by a bacterial infection that usually starts in the mother’s upper genital tract. Immediate and long-term effects of chorioamnionitis for the baby include fetal mortality, neonatal intensive care admission, chronic lung disorders and cerebral palsy. Chorioamnionitis is responsible for approximately half of all preterm births.

This study is part of Kaiser Permanente’s ongoing research to understand the relationship between prenatal conditions and adverse medical outcomes. Earlier this year, a Kaiser Permanente study found the rate of children diagnosed with attention deficit hyperactivity disorder (ADHD) rose dramatically between 2001 and 2010, with non-Hispanic white children having the highest diagnosis rates. Additionally, a Kaiser Permanente study conducted late last year found children who were deprived of oxygen in-utero were significantly more likely to develop ADHD later in life as compared to who are not deprived of oxygen before birth.

Kaiser Permanente can conduct transformational health research in part because it has the largest private patient-centered electronic health system in the world. The organization’s electronic health record system, Kaiser Permanente HealthConnect®, securely connects 9.1 million people, 611 medical offices and 37 hospitals, linking patients with their health care teams, their personal health information, and the latest medical knowledge. It also connects Kaiser Permanente’s researcher scientists to one of the most extensive collections of longitudinal medical data available, facilitating studies and important medical discoveries that shape the future of health and care delivery for patients and the medical community.

The Department of Research & Evaluation conducts high-quality, innovative research into disease etiology, prevention, treatment and care delivery. Investigators conduct epidemiology, health sciences and behavioral research as well as clinical trials. Areas of interest include diabetes and obesity, cancer, HIV/AIDS, cardiovascular disease, aging and cognition, pregnancy outcomes, women’s and children’s health, quality and safety, and pharmacoepidemiology. Located in Pasadena, Calif., the department focuses on translating research to practice quickly to benefit the health and lives of Kaiser Permanente Southern California members and the general population. Visit www.kp.org/research.

About Kaiser Permanente Kaiser Permanente is committed to helping shape the future of health care. We are recognized as one of America's leading health care providers and not-for-profit health plans. Founded in 1945, our mission is to provide high-quality, affordable health care services to improve the health of our members and the communities we serve. We currently serve more than 9 million members in nine states and the District of Columbia. Care for members and patients is focused on their total health and guided by their personal physicians, specialists and team of caregivers. Our expert and caring medical teams are empowered and supported by industry-leading technology advances and tools for health promotion, disease prevention, state-of-the art care delivery and world-class chronic disease management. Kaiser Permanente is dedicated to care innovations, clinical research, health education and the support of community health. For more information, go to www.kp.org/newscenter.